An invention of a prior application was previously filed by the inventor of the present invention relating to this type of electrically conductive glass in the form of Japanese Patent Application No. 2001-400593 (filing date: Dec. 28, 2001).
FIGS. 1-3 show an electrically conductive glass.
In FIG. 1, reference symbol 11 indicates a glass plate. This glass plate 11 is made of soda glass, heat-resistant glass, or quartz glass and so forth having a thickness of about 1 to 5 mm.
On this glass plate 11, a transparent electrically conductive film 12 that covers the entire surface of this glass plate 11 is provided. This transparent electrically conductive film 12 is composed of a thin film of tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO) and so forth that is both transparent and electrically conductive, has a thickness of about 0.2 to 1 μm, and is formed by a thin film formation method such as sputtering or CVD.
A grid 13 composed of a metal film is sealed on this transparent electrically conductive film 12. This grid 13, together with the aforementioned transparent electrically conductive film 12, functions as a pathway for electrons generated in an oxide semiconductor porous film when the electrically conductive glass is used in a dye-sensitized solar cell.
The planar shape of this grid 13 may be, for example, in the form of a lattice as shown in FIG. 2 or in the form of the teeth of a comb as shown in FIG. 3.
In the grid 13 in the form of a matrix as shown in FIG. 2, a countless number of rectangular openings 14, having a width of 450 to 2000 μm and length of 2000 to 20000 μm are formed, and the width of lines 15, which is composed of a metal film extending vertically and horizontally to form a matrix is 10 to 1000 μm. In addition, a wide collecting electrode 16 for collecting electricity is formed extending in the vertical direction on one side.
In the grid 13 in the form of the teeth of a comb shown in FIG. 3, a countless number of lines 15, which form the teeth of a comb, are composed of a metal film and have a width of 10 to 1000 μm, are formed mutually in parallel at an interval of 450 to 2000 μm, a countless number of openings 14 are formed, and a wide collecting electrode 16 for collecting electricity is formed on one of its ends.
This grid 13 is formed by a method such as a plating method and so forth, which is composed of a metal such as gold, silver, platinum, chromium, or nickel, or an alloy of two or more metals thereof, and the thickness of lines 15 is 1 to 20 μm, preferably 3 to 10 μm.
In addition, the numerical aperture of this grid 13 is made to be 90 to 99%. The numerical aperture referred to here is defined as the ratio of the total surface area of lines 15 to the unit surface area.
The total surface resistance of transparent electrically conductive film 12 and the grid 13 (referred to as the sheet resistance) over the entire surface of this electrically conductive glass is 1 to 0.01Ω/□, and is roughly 1/10 to 1/100 of that of transparent electrically conductive glass provided with a transparent electrically conductive film such as an ITO or FTO film. Consequently, this electrically conductive glass can be said to exhibit extremely high electrical conductivity.
Moreover, the entire surface of this type of electrically conductive glass has a high average optical transmittance ranging over the whole surface. Namely, this is because, since the electrically conductivity is improved considerably by the presence of the grid 13, the thickness of the transparent electrically conductive film 12 can be reduced, and since the numerical aperture of the grid 13 is 90 to 99%, there is hardly any blocking of incident light by the presence of the grid 13.
In this manner, the electrically conductive glass of this invention of a prior application has high electrical conductivity and transparency, and a dye-sensitized solar cell in which it is used has possibilities to exhibit a high photoelectric conversion efficiency.
However, in a dye-sensitized solar cell assembled using this electrically conductive glass, there may be backflow of electrons from the grid 13 to the electrolyte between grid 13 and the electrolyte resulting in the flow of leakage current. This is because the energy level of the electrolyte is lower than that of the grid 13, making a comparison between the energy levels of the grid 13 and the electrolyte.
In order to prevent this leakage current, a barrier layer, which is composed of a semiconductor or insulator such as titanium oxide or tin oxide, is further provided at the interface between the grid 13 and the electrolyte, and this barrier layer is expected to be able to inhibit leakage current that flows from the grid 13 towards the electrolyte.
This barrier layer can be formed by a method such as sputtering, complex sintering, spray pyrolysis and CVD.
However, in the case of a barrier layer obtained by this type of thin film formation method, there is the risk of the formation of slight pinholes, and even a single pinhole can result in the flow of leakage current.
In addition, since this barrier layer is also formed on the transparent electrically conductive film 12 other than the grid 13, when used in a dye-sensitized solar cell, the electrons generated in the oxide semiconductor porous film are obstructed from flowing to the transparent electrically conductive film 12, thereby causing a decrease in the amount of generated current or decrease in the fill factor (FF).
Although the barrier layer should only be formed on the grid 13 in order to resolve this problem, the problem of the pinholes remains, and their formation requires a bothersome process such as photolithography, thereby making this disadvantageous in terms of cost.
In addition, nickel is primarily used for the metal serving as the grid 13 in consideration of the manner in which it is formed. However, in the case of providing a grid 13 made of nickel directly on a transparent electrically conductive film 12 comprised of FTO and so forth, the nickel serving as the grid 13 penetrates into the transparent electrically conductive film 12 resulting in deterioration of the transparent electrically conductive film 12 during standing for a long period of time or when subjected to a heat treatment. Consequently, there was also a problem of electrons flowing back into the electrolyte from the transparent electrically conductive film 12, the leakage current flowing between the transparent electrically conductive film 12 and the electrolyte, thereby a significant decrease in the photoelectric conversion efficiency occuring when used in a dye-sensitized solar cell.
Accordingly, an object of the present invention is to provide electrically conductive glass in which a transparent electrically conductive film is provided on a glass and a grid includes a metal film is provided on this transparent electrically conductive film; wherein, when this electrically conductive glass is assembled in a dye-sensitized solar cell or other photoelectric conversion element, the generation of a leakage current flowing from the grid to an electrolyte as well as a leakage current flowing from the transparent electrically conductive film to the electrolyte are prevented.